一，原理
说明：
A为linux服务器a
B为linux服务器b
每台linux都有ssh的服务端和客户端，linux下的ssh命令就是一个客户端
我们常用ssh协议来进行登陆或者是文件的拷贝，都需要密码
A要免密登陆B：
1，需要在a中执行ssh-keygen生成自己的公钥和私钥,生成的文件在.ssh文件中。
2，需要吧a中的公钥copy到b中的中，b进行授权（把公钥中的信息拷贝到“authorized_keys”文件中） 这里只需要一个命令ssh-copy-id 命令
eg：
[eddy@eddy01 .ssh]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/eddy/.ssh/id_rsa):
Enter passphrase (empty for no passphrase): //直接回车
Enter same passphrase again: //直接回车
Your identification has been saved in /home/eddy/.ssh/id_rsa.
Your public key has been saved in /home/eddy/.ssh/id_rsa.pub.
The key fingerprint is:
58:e5:f9:58:27:b5:4e:dc:32:ce:6c:eb:56:ac:89:9b eddy@eddy01
The key's randomart image is:
+--[ RSA 2048]----+
| . . |
| o . o o |
| . o o B .|
| o + O o |
| . S . . *. |
| . .o|
| ..+ |
| .o+ |
| Eo. |
+-----------------+
[eddy@eddy01 .ssh]$ ssh-copy-id eddy02
eddy@eddy02's password:
Now try logging into the machine, with "ssh 'eddy02'", and check in: .ssh/authorized_keys to make sure we haven't added extra keys that you weren't expecting. [eddy@eddy01 .ssh]$ ssh eddy02
Last login: Tue Mar 7 12:25:23 2017 from 192.168.145.1
[eddy@eddy02 ~]$